Add system uptime metric (#1507)

.chloggen/add-system-uptime.yaml

@@ -0,0 +1,17 @@
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the area of concern in the attributes-registry, (e.g. http, cloud, db)
+component: system
+
+# A brief description of the change. Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Add system uptime metric
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+# The values here must be integers.
+issues: [648]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:

docs/system/system-metrics.md

@@ -21,6 +21,8 @@ Resource attributes related to a host, SHOULD be reported under the `host.*` nam
 
 <!-- toc -->
 
+- [General Metrics](#general-metrics)
+  - [Metric: `system.uptime`](#metric-systemuptime)
 - [Processor Metrics](#processor-metrics)
   - [Metric: `system.cpu.time`](#metric-systemcputime)
   - [Metric: `system.cpu.utilization`](#metric-systemcpuutilization)
@@ -73,6 +75,31 @@ Resource attributes related to a host, SHOULD be reported under the `host.*` nam
 > * SHOULD introduce a control mechanism to allow users to opt-in to the new
 >   conventions once the migration plan is finalized.
 
+## General Metrics
+
+### Metric: `system.uptime`
+
+This metric is [recommended][MetricRecommended].
+
+<!-- semconv metric.system.uptime -->
+<!-- NOTE: THIS TEXT IS AUTOGENERATED. DO NOT EDIT BY HAND. -->
+<!-- see templates/registry/markdown/snippet.md.j2 -->
+<!-- prettier-ignore-start -->
+<!-- markdownlint-capture -->
+<!-- markdownlint-disable -->
+
+| Name     | Instrument Type | Unit (UCUM) | Description    | Stability |
+| -------- | --------------- | ----------- | -------------- | --------- |
+| `system.uptime` | Gauge | `s` | The time the system has been running [1] | ![Experimental](https://img.shields.io/badge/-experimental-blue) |
+
+**[1]:** Instrumentations SHOULD use a gauge with type `double` and measure uptime in seconds as a floating point number with the highest precision available.
+The actual accuracy would depend on the instrumentation and operating system.
+
+<!-- markdownlint-restore -->
+<!-- prettier-ignore-end -->
+<!-- END AUTOGENERATED TEXT -->
+<!-- endsemconv -->
+
 ## Processor Metrics
 
 **Description:** System level processor metrics captured under the namespace `system.cpu`.

model/system/metrics.yaml

@@ -1,4 +1,16 @@
 groups:
+  # system.* metrics
+  - id: metric.system.uptime
+    type: metric
+    metric_name: system.uptime
+    stability: experimental
+    brief: "The time the system has been running"
+    note: |
+      Instrumentations SHOULD use a gauge with type `double` and measure uptime in seconds as a floating point number with the highest precision available.
+      The actual accuracy would depend on the instrumentation and operating system.
+    instrument: gauge
+    unit: "s"
+
   # system.cpu.* metrics
   - id: metric.system.cpu.time
     type: metric